This invention relates to a cooling device for a boat engine and more particularly to an improved system for cooling the engine exhaust manifold and exhaust elbow for a marine propulsion system.
As is well known, internal combustion engines are frequently employed for powering watercraft. It is the normal practice, particularly in connection with inboard engines, to provide the engine with a cooling jacket through which coolant is circulated for cooling the engine. In addition, the engine is provided with an exhaust manifold which also has a cooling jacket and which receives coolant from the engine for cooling the exhaust manifold. Exhaust gases are delivered from the exhaust manifold to an exhaust elbow wherein the exhaust gases are discharged to the atmosphere, generally through the body of water in which the watercraft is operating. It is further the common practice to employ a water jacket for the exhaust elbow and the coolant is received from the exhaust manifold, cools the exhaust elbow and then is discharged to the body of water in which the watercraft is operating along with the exhaust gases. Such systems provide a number of advantages. However, the circulation of the engine coolant through the exhaust manifold, particularly when the engine is operating at low temperatures, tends to cause cooling of the manifold and the condensation of liquid therein. The formation of liquid condensation in the interior of the exhaust elbow is particularly disadvantageous because of the possibility that water may be drawn back into the exhaust ports of the engine and damage the internal components of the engine. Arrangements have been provided wherein at least a portion of the coolant is circulated through only a portion of the exhaust elbow and then is returned to the cooling system for the engine before being returned to the body of water through the exhaust elbow. Although such arrangements tend to reduce the likelihood of condensation, they are nevertheless disadvantageous because condensation is still likely to occur, particularly when operating at low engine speeds and low temperatures.
FIG. 1 shows a conventional prior art marine engine cooling sysem and depicts the disadvantages of this type of arrangement. An engine 11 is provided with a cooling jacket 12 through which coolant is circulated by means of an engine driven cooling pump 13. The coolant pump 13 receives water through a conduit 14 from a tank 15 which is divided by an internal wall 16 into a lower chamber 17 and an upper chamber 18. Coolant is delivered from the body of water in which the watercraft is operating to the lower chamber 17 by means of an underwater pickup 19 and auxiliary pump 21 which delivers the coolant through a conduit 22 to the lower chamber 17.
As may be best seen in FIG. 1, the coolant pump 13 delivers water from the chamber 17 to an inlet of the cooling jacket 12 and the return coolant is delivered back to the chamber 17 through a return conduit 23.
A pressure responsive valve 24 is provided in the wall 16 for permitting the chambers 17 and 18 to communicate with each other and to establish a predetermined pressure in the cooling system. This coolant is returned to the body of water in which the watercraft is operating by means of a conduit 25 that extends to a cooling jacket 26 that is formed around an exhaust manifold 27 of the engine 11. The exhaust manifold 27 is shown spaced from the engine 11 but is obviously attached directly to it with its inlet openings in communication with the exhaust ports of the engine. The outlet end of the exhaust manifold 27 communicates with an exhaust elbow 28 via which water from the cooling system as thus far described is discharged to the body of water in which the watercraft is operating in a known manner. A cooling jacket 29 encircles the elbow 28 and receives coolant from the exhaust manifold jacket 26.
A temperature responsive thermostatic valve 31 communicates the chambers 17 and 18 with each other so as to permit the coolant to flow from the lower chamber 17 to the upper chamber 18 once the cooling jacket 12 reaches its normal operating temperature. When this occurs, the water will be discharged back to the body of water in which the watercraft is operating in the aforedescribed manner. It should also be noted that there is provided a restricted opening 32 between the inlet conduit 22 and the pump conduit 14 for restricting the amount of flow and hence the pressure responsive valve 24 will open when the thermostat 31 is closed so that coolant will continuously be circulated through the exhaust manifold 27 and elbow 28 even when the engine is at below its operating temperature. As a result, there is the likelihood of condensation forming in the elbow 28 which can give rise to the undesired results as aforedescribed.
FIG. 2 shows another prior art type of construction wherein an attempt is made to prevent the condensation problems as aforenoted. In connection with this construction, there is provided a further conduit 33 that extends from the chamber 18 to the elbow cooling jacket 29. In conjunction with this embodiment, the exhaust manifold cooling jacket 26 does not receive coolant at all times but the main coolant flow will be through the elbow cooling jacket 29 under low engine temperatures. However, the aforenoted problems still exist.
It is, therefore, a principal object of this invention to provide an improved cooling arrangement for a marine engine wherein the likelihood of condensation in the exhaust manifold and exhaust elbow is substantially reduced, if not completely eliminated.
It is a further object of this invention to provide an improved cooling system for a marine engine that will insure proper and adequate cooling of all components and yet which will also insure that condensation does not occur in the exhaust system, particularly when running at low engine speeds and low temperatures.